The invention is directed toward a process for synthesizing ω-aminoalkanoic acids, or esters thereof, from monounsaturated natural fatty acids, comprising at least one step of forming the unsaturated diacid corresponding to the original fatty acid.
The polyamide industry uses an entire range of monomers consisting of long-chain ω-amino acids, usually called Nylon, characterized by the length of methylene chain (—CH2)n separating the amide functions —CO—NH2—. The following are thus known: Nylon-6, Nylon 6-6, Nylon 6-10, Nylon 7, Nylon 8, Nylon 9, Nylon 11, Nylon 13, etc. These Nylon polymers are often, in the interests of simplification, referred to as PA (for PolyAmide), combining therewith the number of carbon atoms of the molecule: Nylon 8=PA 8, for example.
These monomers are, for example, produced by chemical synthesis using, in particular, as starting material, C2 to C4 olefins, cycloalkanes or benzene, but also castor oil (Nylon 11), erucic or lesquerolic oil (Nylon 13), etc.
The current change in environmental matters is resulting, in the energy and chemistry fields, in preference being given to the exploitation of natural starting materials originating from a renewable source. For this reason, certain studies have been resumed in order to develop, from the industrial point of view, methods using fatty acids/esters as starting material for the production of these monomers.
This type of approach has only a few industrial examples. One of the rare examples of an industrial process using a fatty acid as starting material is that of the production, from ricinoleic acid extracted from castor oil, of 11-aminoundecanoic acid, which is the basis for the synthesis of Rilsan 11°. This process is described in the book “Les Procédés de Pétrochimie” [Petrochemistry processes] by A. Chauvel et al., published by Editions TECHNIP (1986). 11-Aminoundecanoic acid is obtained in several steps. The first consists of a methanolysis of castor oil in a basic medium, producing methyl ricinoleate, which is then subjected to pyrolysis so as to obtain, on the one hand, heptanaldehyde and, on the other hand, methyl undecylenate. The latter is converted into acid form by hydrolysis. The acid formed is then subjected to hydrobromination to give ω-bromo acid, which is converted via amination into 11-aminoundecanoic acid.
Much work has been carried out in order to synthesize 9-aminononanoic acid or 9-aminoazelaic acid, corresponding to Nylon 9, from oleic acid of natural origin.
Mention may be made of the book “n-Nylons, Their Synthesis, Structure and Properties”-1977, Ed. J. Wiley and Sons, chapter 2.9 of which (pages 381 to 389) is devoted to 9-Nylon. This article summarizes the preparations and studies carried out on the subject. Mention is made therein, on page 384, of a process, apparently industrial, developed in Japan using oleic acid which comes from soya oil as starting material. The corresponding description makes reference to the book by A. Ravve “Organic Chemistry of Macromolecules” (1967), Marcel Dekker, Inc., section 15 of which is devoted to polyamides and which mentions, on page 279, the existence of such a process.
To be complete regarding the prior art on the subject, mention should be made of the numerous articles published by E. H. Pryde et al. between 1962 and 1975 in—Journal of the American Oil Chemists' Society—“Aldehydic Materials by the Ozonization of Vegetable Oils” Vol. 39 pages 496-500; “Pilot Run, Plant Design and Cost Analysis for Reductive Ozonolysis of Methyl Soyate” Vol. 49 pages 643-648 and “Nylon-9 from Unsaturated Fatty Derivatives: Preparation and Characterization” Vol. 52 pages 473-477. These articles are essentially devoted to the reaction for reductive ozonolysis of the unsaturated fatty acid. Specifically, since it is well known, as is described in the Ullmann encyclopedia, 5th edition, Vol. A8, pages 523 to 539, that the synthesis of diacids can be obtained by oxidative degradation of unsaturated fatty acids, it is essential that the oxidation reaction be carried out under milder conditions in order to block the reaction and obtain the aldehyde-acid CHO—R—COOH, which is a precursor of the ω-amino acid.